CK Life Sciences is owned by Li Ka-Shing, one of Asia's richest men, worth an estimated $35.7 billion. In 2008, the infrastructure investor bought the Wellington powerlines business, for $785m from Vector.

In January another company owned by the tycoon, Cheung Kong Infrastructure (CKI), reached a $490m deal with Australian-based Ironbridge Capital to buy EnviroWaste, New Zealand's second-largest waste management company.

The deal was subject to Overseas Investment Office approval, and has not yet been cleared.

The purchase is part of a deal where CK Life Sciences paid $150m to buy Cheetham Salt Ltd from the Ridley Corporation, which is Australia's largest producer and refiner of solar salt.

Cheetham owned half the Dominion Salt operation at Lake Grassmere in Marlborough. The other 50 per cent is owned by Cerebos Greggs, part of Singapore-based Cerebos Pacific.

Dominion Salt chief executive Shane Dufaur said the sale would not affect operations at the salt works, near Seddon, which employs between 60 and 85 staff depending on the season.

"We are still 50 per cent owned by Cerebos in Auckland. Nothing is sinister there at all, and we are certainly not looking at selling anything," he said.

The Overseas Investment Office said the deal between Maehtech and Cheetham Salt included its interests in the 1629 hectare Lake Grassmere salt works for $41.7m.

Maehtech intends to grow the Australian and New Zealand salt works business through international expansion.

Lake Grassmere saltworks was founded in 1943 by Christchurch entrepreneur George Skellerup, who also founded the Para Rubber Company.

It is New Zealand's only saltworks, producing about 60,000 tonnes of salt a year, about half the nation's requirements.